Thin-film solar cells poised for big growth
The 'New concepts for high efficiency and low cost in-line manufactured flexible CIGS solar cells' (HIPOCIGS) project team developed and tested a series of new materials and manufacturing processes based on copper indium gallium selenium (CIGS) thin-film technology for producing flexible solar cells. Solar cell production costs are affected by the cost of raw materials. The silicon shortage at the outset of the project has driven material costs up for silicon-based solar cells. This shortage provided the motivation for investment in alternative thin-film technologies. HIPOCIGS researchers tested various low-cost materials and flexible substrates to balance target material quality and cost to find the most advantageous combination. Thin film technology is based on evaporated and/or sputtered material from a target source being coated onto a flexible substrate. The thin films deposited are miniscule — up to micrometres thick — and therefore a small amount of material is needed to achieve the thickness goals. Thus CIGS can dramatically reduce the cost of manufacturing with a high production yield. Investigations covered different types of flexible substrates, including polyimide substrates which were ready for industrial production with the existing state of the art. Unlike glass substrates, these flexible substrates require an external sodium (Na) supply to achieve high efficiencies. Besides different methods for Na supply, HIPOCIGS researchers examined all aspects of CIGS deposition, including the impact of different thicknesses of CIGS absorbers on solar cell performance. After three years of research, excellent cell efficiencies were achieved on different substrates using low-temperature CIGS deposition through co-evaporation. More importantly, higher efficiencies were attained using enamelled steel, where the enamel composition was tailored to act as a source of alkali metals (e.g. Na) as well. By the end of the HIPOCIGS project, the thin-film CIGS solar cells production had made it from the laboratory to the production floor. These results and the knowledge gained during the project should place European photovoltaic research at the forefront in CIGS technology. With CIGS thin film solar cells, the HIPOCIGS team has made an important contribution to developing the next generation of clean energy.
Keywords
Thin film, photovoltaic, solar energy, CIGS, solar cells, silicon, flexible substrate, polyimide, industrial production, glass, steel, enamel, clean energy
